import html
import sys
import urllib.parse


class StackFSM(object):
    """
    Implement a finite state machine that uses a stack to
    manage state.
    """

    def __init__(self):
        self._state_stack = []

    def _current_state(self):
        if len(self._state_stack) > 0:
            return self._state_stack[-1]
        return None

    def update(self):
        fn = self._current_state()
        if fn is not None:
            fn()

    def push_state(self, state):
        self._state_stack.append(state)

    def pop_state(self):
        return self._state_stack.pop()


class Parser(object):

    def __init__(self, document, output=None):
        self._document = document
        if output is None:
            output = sys.stdout
        self._output = output
        self._offset = 0
        self._blanks = 0
        self._fsm = StackFSM()

    def parse(self):
        self._fsm.push_state(self.text_state)
        while self._fsm._current_state() is not None and len(self._document) > self._offset:
            self._fsm.update()

    def text_state(self):
        line = self._document[self._offset]
        if line.strip() == '':
            self._blanks += 1
        else:
            self._blanks = 0
        if line.startswith('```'):
            self._fsm.push_state(self.pre_state)
            self._output.write('<pre>\n')
            self._offset += 1
        elif line.startswith('* '):
            self._fsm.push_state(self.list_state)
            self._output.write('<ul>\n')
        elif line.startswith('=>'):
            self._fsm.push_state(self.link_state)
            self._output.write('<ul>\n')
        else:
            if line.startswith('# '):
                self._output.write('<h1>{}</h1>\n'.format(html.escape(line[2:])))
            elif line.startswith('## '):
                self._output.write('<h2>{}</h2>\n'.format(html.escape(line[3:])))
            elif line.startswith('### '):
                self._output.write('<h3>{}</h3>\n'.format(html.escape(line[4:])))
            elif line.startswith('> '):
                self._output.write('<blockquote>{}</blockquote>\n'.format(html.escape(line[2:])))
            elif line.strip() == '':
                if self._blanks > 1:
                    self._output.write('<br/>\n')
            else:
                self._output.write('<p>{}</p>\n'.format(html.escape(line)))
            self._offset += 1

    def pre_state(self):
        line = self._document[self._offset]
        if line.startswith('```'):
            self._fsm.pop_state()
            self._output.write('</pre>\n')
            self._offset += 1
        else:
            self._output.write(line + '\n')
            self._offset += 1

    def list_state(self):
        line = self._document[self._offset]
        if line.startswith('* '):
            self._output.write('<li>{}</li>\n'.format(html.escape(line[2:])))
            self._offset += 1
        else:
            self._fsm.pop_state()
            self._output.write('</ul>\n')

    def link_state(self):
        line = self._document[self._offset]
        if line.startswith('=>'):
            parts = line[2:].split(None, 1)
            url = parts[0]
            url_parts = urllib.parse.urlsplit(url)
            if url_parts.scheme in ('gemini', ''):
                external = ''
            else:
                external = open('external_link.svg').read()
            if len(parts) == 1:
                text = url
            else:
                text = html.escape(parts[1])
            self._output.write('<li class="link"><a href="{}">{}</a>{}</li>\n'.format(url, text, external))
            self._offset += 1
        else:
            self._fsm.pop_state()
            self._output.write('</ul>\n')